VT240 repair

[retrobits]

Hi all,

I have a VT240 terminal with keyboard, VT241A color monitor and video cable. It is not functioning. When the terminal is powered up, the power supply fan turns on, and a blank screen appears on the monitor. There are no characters displayed, but when the terminal is on, the video monitor displays a white rectangle instead of just the white field it shows at power up (brightness turned way up). I hear a speaker keyclick for the first three keys I press, then nothing. Pressing SET UP does not display anything.

The terminal controller board is the full-size version. I've reseated the socketed chips and power supply connection, and blown out all the dust. The switches on the VT241A monitor are set to 75 ohm, INT (for the 3-wire RGB cable).

The service guide says to replace the terminal controller board, but this is 2012 and I don't have a spare.

Any thoughts on diagnosis/repair? It would be great to be able to fix it. While dirty, the terminal is otherwise in great cosmetic shape, and would clean up beautifully. And it seems that the most likely failure part, the color monitor, is still alive and kicking.

Thanks for any help and ideas,

- Earl

 

[Lou - N2MIY]

Earl,

I have done component level repairs on one of my two VT240s. I have the tech manual and the print set (for one of the two etch revs of boards).

Do you have proper tools and experience for component level repairs? You're going to need desoldering tools, scope, etc.

Do you have a VR201 you can connect instead of the VR241? Does the terminal send anything out the serial port when you press keys on the keyboard? Have you checked the power supply voltages?

Lou

 

[retrobits]

Hi Lou,

Thanks for responding. I do not have the proper tools or experience myself for component level repair; however, I have a couple of friends who may be able to assist. Do you happen to know if those VT240 service documents/print sets are online anywhere? I didn't see them on Bitsavers or vt100.net.

I do not have the monochrome monitor - only the color one. Do you know if the output from the composite video output connector is a "standard" NTSC signal - that is, could I connect it to a generic mono video monitor, given the right cable (BNC to RCA)?

I'll check these two things right away:

- Verify proper voltages from the power supply, using the service guide as a reference
- Verify if pressing keys causes any serial output

Thanks!

- Earl

 

[Lou - N2MIY]

Earl,

The print set is available online, but takes a little work to find. google "MP-01807-01" and you will find what you seek.

The tech manual is not online. I have it on fiche and photographed the fiche. With the assistance of another dec "Microfiche Underground" participant, we have it converted to .PDF (although it is quite large.)

If you are able to get one of your friends to work on this, I could mail you a CD of the tech manual.

The BNC on the back is indeed RS-170 video. Try looking at it on your TV set.

Lou